There are various ways by which microsleep episodes can be identified. Some experts define microsleep according to behavioral criteria (eyelids closure), while others rely on electroencephalogram markers such as a 3-15 second episode (shorter durations would be difficult to visually detect and longer times would qualify as sleep onset.) during which 4-7 Hz (theta wave) activity replaced the waking 14-20 Hz (alpha wave) background rhythm.
Microsleep, subjectively related to the sensation of "nodding off', is associated with the interruption of the blinking artifacts characteristic of full wakefulness. During microsleep events, attention lapses can impair the ability to detect and respond to crucial stimuli and events. For example, microsleeps (or microsleep episodes) can become extremely dangerous when occurring during situations which require continual alertness, such as driving a motor vehicle or operating machinery. People who experience microsleeps usually remain unaware of them, instead believing themselves to have been awake the whole time, or feeling a sensation of 'spacing out'. The sleepy driver is at very high risk of having an accident during a microsleep episode. Many accidents have occurred because of microsleep episodes. Microsleep, subjectively related to the sensation of "nodding off ', is associated with the interruption of the blinking artifacts characteristic of full wakefulness. During microsleep events, attention lapses can impair the ability to detect and respond to crucial stimuli and events. For example, microsleeps (or microsleep episodes) can become extremely dangerous when occurring during situations which require continual alertness, such as driving a motor vehicle or operating machinery. People who experience microsleeps usually remain unaware of them, instead believing themselves to have been awake the whole time, or feeling a sensation of 'spacing out'. The sleepy driver is at very high risk of having an accident during a microsleep episode. Many accidents have occurred because of microsleep episodes.
Clearly, the ability to detect microsleep events would be useful as a means of alerting and warning drowsy drivers of such events. Clearly, the ability to detect microsleep events would be useful as a means of alerting and warning drowsy drivers of such events.
Several studies have used "quantitative" EEG methods to identify driver sleepiness. Theta power (EEG waves), and the frequency of theta bursts typically increase during prolonged driving, and are associated with poor driving performance. Disadvantageously, these techniques typically average EEG activity over several seconds (up to 1 minute), and therefore could not be used to detect brief microsleep events of between 3 seconds and 15 seconds. Several studies have used "quantitative" EEG methods to identify driver sleepiness. Theta power (EEG waves), and the frequency of theta bursts typically increase during prolonged driving, and are associated with poor driving performance. Disadvantageously, these techniques typically average EEG activity over several seconds (up to 1 minute), and therefore could not be used to detect brief microsleep events of between 3 seconds and 15 seconds.
A variety of physiological measures have been proposed to alert drivers to the onset of drowsiness. A variety of physiological measures have been proposed to alert drivers to the onset of drowsiness.
One of the most investigated is PERCLOS (or PERcent CLOSure), which measures drowsiness as the percent of time a driver's eyes are closed over a One of the most investigated is PERCLOS (or PERcent CLOSure), which measures drowsiness as the percent of time a driver's eyes are closed over a
time period. When a sufficient number of open/closed patterns are obtained, PERCLOS will trigger an alarm. PERCLOS works at percentages greater than 80%, which typically means that within 1 minute, the eyes of the individual must be closed for 48 seconds before an alarm is triggered. Clearly, this delay in unacceptable in tasks such as driving a vehicle because by the time PERCLOS activates the alarm, the driver will already have either fallen asleep, or be on the verge of falling asleep. Therefore, disadvantageously PERCLOS is too slow a system to allow preventive actions to be taken before an individual, such as a driver, experiences the first signs of sleepiness. time period. When a sufficient number of open / closed patterns are obtained, PERCLOS will trigger an alarm. PERCLOS works at percentages greater than 80%, which typically means that within 1 minute, the eyes of the individual must be closed for 48 seconds before an alarm is triggered. Clearly, this delay in unacceptable in tasks such as driving a vehicle because by the time PERCLOS activates the alarm, the driver will already have either fallen asleep, or be on the verge of falling asleep. Therefore, disadvantageously PERCLOS is too slow a system to allow preventive actions to be taken before an individual, such as a driver, experiences the first signs of sleepiness.
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